The subject matter disclosed herein relates to accounting for deviations in masks (photomasks) used in the fabrication of integrated circuits. More specifically, the subject matter disclosed herein relates to accounting for deviations in photomasks and including the effects of these deviations in optical proximity correction verification (OPCV) simulations.
In the case that an integrated circuit process mask (e.g., a photomask) is not printed at its target critical dimension (CD), or the structure used for controlling the wafer lithography line is not at its target dimension on the mask, the lithography process may compensate for these errors by adjusting the exposure dose used. However, where the effect of changing dose is not equivalent to the change in mask critical dimensions for all structures, optical proximity correction verification (OPCV) may be inaccurate. For example, if a control structure is 2 nanometers larger than target on a mask, and the dose is reduced in order to make the control structure print at its target, then other structures may be printed at altered dimensions (e.g., either larger or smaller), depending upon the mask error enhancement factors (MEEF) and the exposure latitude of those structures.
Prior approaches assume that changing the exposure dose in-line will compensate exactly for changes in the mask critical dimension. However, when this assumption is invalid, OPCV may not account for these errors that could cause yield and reliability issues in the underlying printed circuit.